1. Field of the Invention
The present invention relates to a process for producing an aliphatic copolyesteramide, an aliphatic copolyesteramide and tubing molded from the aliphatic copolyesteramide, the tubing having excellent flexibility, toughness, shapability, chemical resistance, heat resistance, hydrolysis resistance and fatigue resistance.
2. Description of the Prior Art
Recently, flexible thermoplastics such as plasticized polyvinylchloride, plasticized polyamides such as nylon 11 and nylon 12, polyurethane and polyetherester elastomer have been investigated for molding into tubing, pipes and hoses employed as various pressure hoses, such as hydraulic hoses and oil pressure hoses, vacuum hoses and automobile parts such as fuel line tubing and brake line tubing. Such tubing has an advantage in that it does not need vulcanization which is required for tubing molded from natural rubber and synthetic rubber and that it has excellent moldability. However, the abovementioned materials have the following disadvantages. That is, polyvinylchloride and polyurethane are inferior in heat resistance, polyurethane is inferior in hydrolysis resistance, polyetherester elastomer is inferior in chemical resistance, polyamide is inferior in flexibility, and plasticized polyamide has a serious tendency of exudation of plasticizer.
It has now been found that an aliphatic copolyesteramide comprising specified components can have a low glass transition temperature and be formed into tubing having excellent flexibility, toughness, chemical resistance and hydrolysis resistance without the addition of plasticizer. It has been known that aliphatic copolyesteramide can be prepared by polymerization of a mixture comprising diamines, dicarboxylic acids, polyhydric alcohols and/or aminocarboxylic acids or lactams in the presence of water under an internal pressure of above 14 bars in the first stage and under a reduced pressure in the second stage (for example in U.S. Pat. No. 4,101,524).
However, a copolyesteramide having high viscosity and good qualities which are necessary to provide tubing exhibiting excellent shapability and mechanical properties, especially cold impact strength, cannot be obtained according to the above-described process. Because inactivation of the catalyst occurs in the presence of water as well as with the high internal pressure in the first stage, prolonging the total time for polymerization degradation, such as partial thermal decomposition of the copolyesteramide results.